Such test stands, e.g., vehicle, engine or transmission test stands, are used by the automobile industry, among others, and support research and development with the help of functional tests, endurance trials for the mechanical load test as well as consumption, exhaust gas, and noise or climate analyses, for example. These test stands simulate the operation of a vehicle or of vehicle components under different environmental or application conditions. The vehicle or the vehicle components, which are to be tested, can be coupled on the test stand to a load device, e.g., an asynchronous machine, a hydraulic dynamometer, or an eddy current brake. The load device simulates the load, against which the engine must operate in actual real operation.
In addition to numerous measured variables, the torque acting between the vehicle and the load device is of particular importance. For this purpose, the load device is supported to oscillate, so that the torque, which the vehicle applies to the load device, must be supported on the housing of the load device, which is supported to oscillate. A lever arm, on the outer end of which provision is made for a force-measuring device (to measure the force that is transmitted via the lever arm), is attached to the housing of the load device. The torque, which acts on the load device and which is thus output by the vehicle, can be determined in this manner by the measured force and the length of the lever arm, which is effective here.
Due to the fact that high demands are made on the accuracy of the torque measurement, the force-measuring device must be calibrated from time to time.
In the case of a roller-type test stand, the rollers must be freely rotatable for calibrating. A certain reference torque, the value of which is compared to the torque measured by the test specimen torque transducer (lever arm and force-measuring device), is then applied to the load device or to the housing of the load device, respectively, to carry out an adjustment, in particular, of the force-measuring device, if necessary.
The reference torque must be predetermined or preselected, respectively, with the highest possible accuracy. A calibrating method, which is based on the double lever principle, e.g., and which is described in European Patent Application 1,293,765, proved to be effective for this purpose. In this reference, provision is made on the housing of the load device (a dynamometer) for a lever arm, at the end of which the force-measuring device (which is to be calibrated) is disposed. Opposite the lever arm, a second lever arm must be attached to the housing of the load device on the other side of the housing for carrying out the calibration, provision being made on the housing for a load device in the form of a hydraulic or a pneumatic cylinder. The cylinder applies a force to the additional lever arm. The force is determined by a reference load cell. In the event that the load device is otherwise not loaded by any further external load, the actual force-measuring device must, accordingly, measure a corresponding value, which is a function of the lever ratios. If this is not the case, the force-measuring device must be adjusted.
In the case of the calibrating apparatuses known from the state of the art, a considerable additional technical effort, e.g., in the form of additional lever arms, is required in each case. In addition, it is possible for the load device to be lifted out of its supports due to unsuitable force introduction, whereby the calibrating result can be impacted or distorted, respectively.